The JP 2007-331871 A has disclosed a double-decker elevator system. The known elevator comprises a car frame, in which two elevator cars are arranged vertically one above the other. Each of the two elevator cars is positioned on a carrier with rope pulleys. Furthermore the car frame has a drive unit arranged on it with a hoist rope running around it. The hoist rope is guided on one side around the rope pulleys of the carrier of the one elevator car and, on the other side, around the rope pulleys of the carrier of the other elevator car. By operating the hoist rope by means of the drive unit, the suspended elevator cars can be raised and lowered relative to the car frame. In this way it is possible to position the two elevator cars differently within the car frame.
The double-decker elevator known from the JP 2007-331871 A has the disadvantage that the drive unit arranged on the car frame requires a relatively large amount of space. This means that the drive unit must be sufficiently powerful because different tensile forces may be acting on the hoist rope on one side with the one elevator car and on the other side with the other elevator car. This may be due to, among others, a difference in loading of the two elevator cars. In addition there are large forces acting upon a traction sheave of the drive unit, when both elevator cars are loaded to a maximum. The drive unit must therefore be very powerful in order to be able to absorb the forces and torques occurring, including for maximum or extremely different loads, and to perform the desired adjusting movement.